Afghanistan's president has appealed for Pakistan's help in negotiating a peace deal with Taliban militants before a summit that will also include Iran's leader.

The meetings in Islamabad come at a time when momentum for peace talks with the Taliban seems to be growing, even as all parties to a stuttering process marked by intense mistrust say success in ending the 10-year war in Afghanistan is far from certain.

President Hamid Karzai told The Wall Street Journal that talks among the US, the Afghan government and the Taliban had taken place in the past month.

If true, it would mark a significant development because until now the Taliban had said it would negotiate only with the Americans, contending that Mr Karzai was a puppet leader and that their movement was the legitimate ruler in Afghanistan.

Taliban spokesman Zabiullah Mujahid denied negotiations had already taken place. "The Taliban did not talk with the Kabul government anywhere," he said in a statement.

Pakistan is regarded as a key player in any peace process because its historical ties with the Taliban and other insurgents mean Islamabad could help bring them to the table or be a spoiler. The Taliban leadership is widely believed to be based in Pakistan, and under some influence of the country's security establishment.

Relations between Pakistan and Afghanistan have been badly strained, but the meeting between Mr Karzai and Pakistan's President Asif Ali Zardari suggested that ties were improving.

An Afghan statement said the leaders had agreed to restart a joint peace commission that was shelved after the assassination last year of Afghanistan's envoy to Taliban peace talks in Kabul. Afghan officials had accused Pakistan of playing a role in the killing - claims it denied.

In a statement, Mr Zardari said Mr Karzai said at the meeting that Pakistan's support "was critical to the success of the Afghan owned and Afghan led peace process" and that both countries should co-operate for peace.

Iranian president Mahmoud Ahmadinejad arrived in Islamabad and met Mr Zardari separately. The two men discussed a proposed pipeline that would deliver natural gas from Iran to Pakistan, according to a statement from Mr Zardari.